[DonRotolo]

In most cases, you need the full hub (the part surrounding the hole in the middle) of the sprocket to mount it to a shaft. You can also make the hole bigger, or drill holes to bolt the sprocket to something.

In any case, you cannot depend upon friction or an adhesive to prevent the sprocket from spinning on the 'shaft' - you must use a roll pin, or set screw, or square/woodruff key, or some other method.

Considering that, you might just use the whole sprocket. As others have stated, if you really can't afford a sprocket, ask here. Many teams have extras lying around, and will happily share with you.

As maltz1881 stated, success will be getting a robot that passes inspection and can move on the field. Everything after that is gravy.

It's not about the robot - search on that phrase to understand what that means.

Don